Axial piston machine with adjustable swash plate

ABSTRACT

An axial piston machine wherein the swash plate is held against rotation with the cylinder block and is tiltable to both sides of its neutral position by a mechanical, fluid-operated, electrical or electronic system. The swash plate is always tilted about an axis which intersects the axis of that piston in the cylinder block which is nearest to the valve plate to thus maintain the volumes of liquid-filled spaces between the pistons in their foremost positions and the valve plate at a minimum.

United States Patent [1 1 Bosch [111 3,733,970 [4 1 May 22,1973

[54] AXIAL PISTON MACHINE WITH ADJUSTABLE SWASH PLATE [75] Inventor: Paul Bosch, Ludwigsburg, Germany [73] Assignee: Robert Bosch GmbH, Stuttgart, Germany [22] Filed: July 20, 1971 [21] Appl. No.: 164,306

[30] Foreign Application Priority Data July 29, 1970 Germany ..P 20 37 635.6

[52] U.S. Cl ..91/506, 417/217 [51] Int. Cl ..F0lb 13/04 [58] Field of Search ..417/222, 217, 274, 417/275; 91/505, 506, 475; 92/605; 74/831 [56] References Cited UNITED STATES PATENTS 2,231,100 2/1941 Wahlmark ..91/506 1,521,884 1/1925 Higgins ..91/475 3,463,087 8/1969 Grant ..91/506 2,964,234 12/1960 Loomis ..74/831 Primary ExaminerWilliam L. Freeh Assistant Examiner-G. P. LaPointe Attorney-Michael S. Striker [57] ABSTRACT An axial piston machine wherein the swash plate is held against rotation with the cylinder block and is tiltable to both sides of its neutral position by a mechanical, fluid-operated, electrical or electronic system, The swash plate is always tilted about an axis which intersects the axis of that piston in the cylinder block which is nearest to the valve plate to thus maintain the volumes of liquid-filled spaces between the pistons in their foremost positions and the valve plate at a minimum.

15 Claims, 4 Drawing Figures PATENTE HAY 21573 3, 7 33 9 7 0 sum 2 OF 2 Fig. 3

Fig.4

{ Ill mlil Paul Ea /50W his 147 f ORA/5 y AXIAL PISTON MACHINE WITH ADJUSTABLE SWASH PLATE BACKGROUND OF THE INVENTION The present invention relates to axial piston machines in general, and more particularly to improvements in axial piston machines with adjustable tilting or swash plates. Still more particularly, the invention relates to improvements in axial piston pumps or motors wherein the swash plate is held against rotation with reference to the cylinder block and is tiltable with reference to the axis of the drive shaft for the cylinder block to thereby change the throughput of fluid which is being conveyed by the pistons.

Axial piston machines are subjected to very high thermal stresses, especially when the pistons in their cylinder blocks are called upon to convey a liquid at a very high pressure and in relatively small quantities, i.e., when the swash plate is inclined in such a way that the pistons can perform relatively short working strokes. Such thermal stresses are due mainly to the presence of certain quantities of liquid in those portions of bores for the pistons which are adjacent to the valve plate. It is well known that the pistons in the cylinder block of an axial piston machine cannot displace all of the liquid which is contained in the space between the pistons and the valve plate. This is due to the fact that, even when it assumes its foremost position with reference to the valve plate, each piston of an axial piston machine is still separated from such valve plate by a certain distance which is necessary for manufacturing purposes and for certain other reasons. Whenever a bore moves from registry with the high-pressure groove into registry with the low-pressure groove of the valve plate, some of the liquid which is contained in the foremost portions of bores for the pistons flows into the low-pressure groove. The high potential energy in the form of heat which is stored'in such liquid is permitted to enter the low-pressure conduit which is connected with the low-pressure groove of the valve plate to thus adversely affect the operation of the axial piston machine, especially if the latter is used as a pump. The inflowing liquid is subjected to excessive heating action before it reaches the low-pressure groove in the valve plate, and such heating brings about a reduction in viscosity and the elimination of films of lubricant which must be present on the pistons as well as between the front end face of the rotating cylinder block and the adjacent surface of the valve plate. The elimination of such films of lubricant can interfere with further operation of the axial piston pump. Similar problems can arise when the machine is used as a motor.

US Pat. No. 2,964,234 to Loomis discloses a constant clearance volume axial piston pump wherein the volume of liquid which remains in a bore of the cylinder block when the respective piston is moved to a position at a minimum distance from the valve plate is reduced to a minimum by the provision of adjusting means which insures that the swash plate is tiltable to and from a large number of positions but always in such a way that the'volume of the aforementioned undesirable space for one of the pistons (namely, the piston nearest to the valve plate) is held toa minimum. However, such adjustment is achieved at the expense of restricting the extent of pivotal movement of the swash plate. Thus, the swash plate is movable only in one direction from a neutral position in which the axial piston pump does not convey any liquid. If it is desired to change the direction of liquid How, the direction of rotation of the cylinder block must be changed by resorting to a suitable transmission or to a reversible electric motor which causes the axial piston machine to change the direction of liquid flow when the machine is used as a pump. If the axial piston machine. is used as a motor, it must be equipped with a system of special control valves. Thus, a reduction in the volume of undesirable space for liquid in piston bores close to the valve plate is achieved at the additional expense of using a special motor when the machine is used as a pump and the additional cost of using special valves when the machine is used as a motor. Still further, the swash plate is free to rotate in the housing of the machine and, therefore, the patented axial piston machine must be provided with costly and complicated balancing means for the mass of the revolving swash plate. Also, the adjusting means for the swash plate is quite complicated and prone to malfunction.

SUMMARY OF THE INVENTION An object of the invention is to provide an axial piston pump or motor wherein the clearance for liquid between the pistons and the valve plate is held to a minimum in all positions of the swash plate without in any way affecting the adjustability of the swash plate.

Another object of the invention is to provide an axial piston machine with novel means for effecting adjustments in the position of the swash plate without changing the volume of liquid confined between the piston which dwells in its foremost position and the valv plate.

A further object of the invention is to provide an axial piston machine with novel means for adjusting a swash plate which does not rotate with the cylinder block.

An additional object of the invention is to provide an axial piston machine with compact,'simple and rugged adjusting means which can move the swash plate to both sides of the neutral position to eliminate the need for a reversible motor when the machine is used as a pump and to eliminate the need for spacial valve groups when the machine is used as a motor. I

The invention is embodied in an axial piston pump or motor which comprises a cylinder block rotatable in a housing about a predetermined axis and having a plurality of preferably equidistant axially parallel openended bores, pistons reciprocably received in the bores of the cylinder block, a valve plate mounted adjacent to the cylinder block and serving to seal the open ends of the bores as well as to provide paths for the flow of a hydraulic fluid to and from the bores, a swash plate tiltable in the housing with reference to the axis of rotation of the cylinder block to both sides of a neutral position to thereby change the extent of movement of the pistons with reference to the cylinder block in a direction away from the valve plate while maintaining the pistons at a predetermined minimum distance from the valve plate when it assumes the neutral position, one of the pistons in the cylinder block being'always located at such minimum distance from the valve plate whenever the swash plate is tilted from its neutral position, means for holding the swash plate against rotation with reference to the housing, i.e., against rotation with the cylinder block, and novel adjusting means for changing the inclination of the swash plate with reference to the axis of rotation of the cylinder block.

The adjusting means comprises a pair of tilting members which are preferably movable in parallelism with the axis of rotation of the cylinder block and are operatively connected with the swash plate at points located diametrically opposite each other with reference to the axis of rotation of the cylinder block and mechanical, hydraulic, pneumatic, electrical, electromagnetic or electronic means for moving at least one of the tilting members to thereby tilt the swash plate about an axis which intersects the axis of the one piston (namely, of a piston which dwells in an end position nearest to the valve plate) to thus insure that the axial position of the one piston remains unchanged in spite of the tilting of the swash plate.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved axial piston machine itself, however, both as to its construction and its mode of operation, together with additional features and ad- .vantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic axial sectional view of an axial piston machine with mechanical adjusting means for the swash plate;

FIG. 2 is a fragmentary axial sectional view of a second axial piston machine with fluid-operated adjusting means for the swash plate;

FIG. 3 is a schematic partly elevational and partly axial sectional view of a third axial piston machine with electrically operated adjusting means for the swash plate and FIG. 4 is a schematic partly elevational and partly axial sectional view of a fourth axial piston machine with electronically operated adjusting means for the swash plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The axial piston machine of FIG. 1 comprisesa hollow cylindrical housing or body 1 the right-hand end of which is provided with a removable cover 3 secured thereto by screws 2 or analogous fasteners. The drive shaft 4 of the machine extends axially through the cover 2 and into the interior of the housing 1 and is secured to a cylinder block 9. The inner end portion of the drive shaft 4 rotates in a bearing sleeve 5 which is recessed into the valve plate 16 of the machine. The drive shaft 4 rotates in an antifriction bearing 6 which is mounted in the central portion of the cover 3, and

' the shaft is sealingly surrounded by an annular packing 8. The bearing '6 has two races provided with ringshaped grooves for spherical rolling elements. The outer end portion 7 of the drive shaft 4 is connected with a prime mover or with a driven part, not shown.

A median portion 10 of the drive shaft 4 is provided with one or more axially parallel splines extending into complementary axially parallel flutes of the cylinder block 9 so that the latter shares all angular movement of the drive shaft. A helical spring 11 is mounted in an enlarged portion of an axial bore in the cylinder block 9 and reacts against a disk 13 which abuts against a shoulder 12 of the drive shaft 4. The purpose of the spring 11 is to permanently bias the left-hand end face of the cylinder block 9 against the adjacent right-hand end face of the valve plate 16 which latter is shown as forming an integral part of the housing 1. The left-hand end convolution of the spring 11 bears against a washer 14 which abuts against a split ring 15 recessed into the internal surface of the cylinder block 9. Thus, the righthand end convolution of the spring 1 l bears against the drive shaft 4 through the intermediary of the disk 13 and shoulder 12, and its left-hand end convolution acts against the cylinder block 9 through the intermediary of the washer 14 and split ring 15.

The cylinder block 9 is provided with equidistant axially parallel open-ended bores 17 for pistons 18 which are sealingly received and slidable in the respective bores 17. The open ends of the bores 17 are sealed by the valve plate 16. The outer (right-hand) end portions 19 of the pistons 18 are provided with pivotably mounted shoe-like followers 20 which track the adjacent surface of a tilting plate or swash plate 23. The bores 17 are provided with internal shoulders 22 which serve as abutments for the left-hand end convolutions of helical springs 21 which bias the followers 20 of the respective pistons 18 against the swash plate 23. The left-hand end portions of the pistons 18 are preferably provided with axially extending blind bores to receive the major portions of the respective springs 21. The swash plate 23 has a radially outwardly extending projection 24 which is received in an axially parallel internal groove 25 of the housing 1 to hold the swash plate against rotation with reference to the housing.

In accordance with a feature of the present invention, the axial piston machine is provided with novel adjusting means for tilting the swash plate 23 in such a way that the limit of the working strokes of pistons 18 (in a direction toward the valve plate 16) remains unchanged. This insures a constant clearance volume operation of the machine. The adjusting means comprises a pair of links 26 which are disposed diametrically 0pposite each other with reference to the axis of the drive shaft 4. The links 26 extend into radially inwardly extending slots of the swash plate 23 and are secured to the latter by pivot pins which are tangential to the cylinder block 9 and normal to and crossing in space with the drive shaft 4. The links 26 are further articulately connnected with two tilting members 29, 29' which constitute the piston rods of two adjusting pistons 27, 27 (hereinafter called adjusting plungers to avoid confusion with the pistons 18). The plungers 27, 27' are respectively reciprocable in cylinder chambers 28, 30 machined into the housing 1. The axes of the adjusting plungers 27, 27 are located in a plane which also includes the axis of the drive shaft 4 and the link 26. Each of the chambers 28, 30 has a smaller-diameter extension which sealingly but slidably receives the respective piston rod or tilting rod 29, 29'.

The left-hand end faces of the adjusting plungers 27, 27 are respectively provided with axially extending blind bores 31, 31' for portions of control pistons 32, 32' which carry roller followers extending into suitably configurated grooves 33, 33' of two plate earns 34, 34. The earns 34, 34' are pivotably mounted on a bracket 35 secured to or provided on the left-hand portion of the housing 1. When the earns 34, 34' are pivoted with reference to the bracket 35, the control pistons 32, 32' perform axial movements to thereby change the axial positions of adjusting pistons 27, 27' and the inclination of the swash plate 23. The pistons 32, 32' and the cams 34, 34' constitute a follow-up or remote control 1 Qdevice for the swash plate 23.';-The cams 34, 34 are coupled to each other by a connecting rod 38 so that they can be pivoted as a unit. The pivot axes of the cams 34, 34' are parallel to pivot axes of the links 26 on the swash plate 23.

Each bore 17 of the cylinder block 9 has a smallerdia'meter open-ended extension 39 which terminates at the left-hand face of the cylinder block 9. The axes of the extensions 39 are located on a circle whose center is on the axis of the drive shaft 4. The valve plate 16 is formed with two kidney-shaped grooves or recesses 40, 41 having their centers of curvature located on the axis of the drive shaft 4. When the cylinder block 9 is 1'0- tated by the drive shaft 4, the extensions 39 of the bores 17 alternately register with and travel along the grooves 40 and 41. The bores 42 and 43 of the valve plate 16 respectively communicate with the grooves 40 and 41. One of these bores is connected with a source of oil or another hydraulic fluid and the other bore serves to convey pressurized fluid which is drawn by the pistons 18 from one of the grooves 40, 41 via the respective extensions 39 and is expelled into the other groove when the machine operates as a pump. in the illustrated solid-line position of the swash plate 23, the lower bore 43 serves to admit hydraulic fluid into the groove 41 and the groove 40 serves to supply pressurized fluid to the bore 42. If the inclination of the swash plate 23 is changed to the phantom-line position of FIG. 1, the extensions 39 of bores 17 in the rotating cylinder block 9 will draw hydraulic fluid from the bore 42 through the intermediary of the groove 40 and will deliver pressurized fluid to the bore 43 by way of the groove 41.

As is well known, the extent of working strokes of the pistons 18, and hence the throughput of the machine, depends on the inclination of the swash plate with reference to a plane which is normal to the axes of the drive shaft 4. Such inclination can be adjusted by the links 26 in response to appropriate adjustment of the cams 34, 34 whereby the control pistons 32, 32' displace the adjusting plungers 27, 27' and their piston rods 29, 29' with reference to the cylinder chambers 28 and 30. The connecting rod 38 insures that each angular adjustment of the cam 34 brings about a corresponding angular adjustment of the cam 34' and vice versa.

When the machine of FIG. 1 is operated as a pump, the throughput of the pump can be reduced to zero by moving the swash plate 23 to a position in which its lefthand end face is normal to the axis of the drive shaft 4 so that the pistons 18 merely rotate with the cylinder block 9 but perform no axial movements. All of the pistons 18 are then held in identical axial positions. In order to insure that the volume of the undesirable liquid-filled spaces to the left of the pistons 18 is held to a minimum, the neutral position of the swash plate 23 (in which the pistons 18 do not move axially) is selected in such a way that the distance between the pistons 18 and the valve plate 16 is reduced to a minimum, i.e., that the entire swash plate is as close to the cylinder block 9 as possible. The axial positions of the adjusting pistons 27, 27' with reference to the cylinder chambers 28, 30 are then identical. The volume of the liquid-filled portions of bores 17 in the cylinder block 9 is then reduced to a value which cannot be reduced any further due to the presence of springs 21 and extensions 39.

If the machine is to be thereupon adjusted so as to start the delivery of pressurized hydraulic fluid, the swash plate 23 is tilted about the point where one of the followers 20 pivots with reference to the corresponding piston 18. This insures that the leftmost ends of work ing strokes of the pistons 18 remain unchanged irrespective of the inclination of the swash plate 23. If the swash plate 23 is thereupon tilted to change its inclination and to thus change the output of the machine, the adjusting plungers 27, 27' again insure that the tilting takes place without changing the axial position of the piston 18 which dwells in its leftmost position. In this way, the clearance between the valve plate 16 and the piston 18 which has completed its working stroke to expel pressurized fluid into the groove 40 or 41 remains unchanged. It will be noted that the links 26 are outwardly adjacent to the circle formed by the pistons 18; therefore, each angular adjustment of the swash plate 23 involves a leftward movement of one of the control pistons 32, 32' and a rightward movement of the other control piston. Such movements of the control pistons 32, 32' in opposite directions are insured by the connecting rod 38 and by the configuration of grooves 33, 33' in the cams 34, 34. The reference character A denotes one of the points about which the swash plate 23 must be tilted in order to change the output of the machine; this point A coincides with the point where one of the followers 20 pivots with reference to the end portion 19 of the associated piston 18.

If the direction of fluid flow between the bores 42, 43 is to be reversed, the earns 34, 34' are pivoted as a unit to such an extent that the swash plate 23 moves beyond the neutral position and changes its inclination with reference to the axis of the drive shaft 4 from an acute angle to an obtuse angle or vice versa. The inclination of the swash plate 23 is always changed in such a way that the axial position of the one or the other of the two pistons 18 shown in FIG. 1 remains unchanged, namely, that one of the followers 20 invariably compels the respective piston 18 to assume its leftmost position at a minimum distance from the valve plate 16 to thus insure that the volume of the liquid filled space in the associated bore 17 between the left-hand end face of the respective piston 18 and the valve plate 16 is maintained at a minimum.

The cams 34, 34' can be adjusted mechanically, for example, through the intermediary of the connecting rod 38 or by means of a fluid which is admitted into the chambers 28, 30 to change the axial positions of the adjusting plungers 27, 27'. The remote control system can utilize an auxiliary pump for a pressurized fluid or it may receive pressurized fluid from the axial piston pump.

The plate earns 34, 34' can be replaced with cylindrical cams having circumferential grooves for the followers of control pistons 32, 32.

FIG. 2 illustrates modified adjusting means for the swash plate 23 (not shown). This adjusting means employs two adjusting valves having rotary valve members or spools 49 one of which is shown in FIG. 2. Each such valve member 49 can regulate the position of one of two adjusting plungers 47 which are articulately connected with the swash plate in the same way as shown at 26 in FIG. 1 for the connections between the swash plate 23 and the piston rods 29, 29 of the adjusting plungers 27, 27. The illustrated adjusting plunger 47 is a differential piston which is reciprocable in the cylinder chamber 46 of a housing 45 having an end wall 45a which can be detached to afford access to the chamber 46 and to the chamber for the other adjusting plunger 47. The piston rod or tilting rod 48 of the plunger 47 is coupled to the swash plate by a link corresponding to one of the links 26 shown in FIG. 1.

The valve member 49 is turnable in an axial bore 50 of the adjusting plunger 47 and in a bore 51 of the end wall 45a. A flange 52 at the left-hand end of the valve member 49 is confinedto angular movement in the bore 51 by a split ring 54 which is recessed into the internal surface of the end wall 45a. The split ring 54 maintains the flange 52 in abutment with a shoulder 53 of the end wall 45a so that the valve member 49 is held against axial movement. An O-ring 55 is inserted into the end wall 45a to surround the valve member 49 and to prevent leakage of fluid from a compartment 63 forming the left-hand portion of the cylinder chamber 46 in the housing 45. An eccentric crank pin 57 of the flange 52 is articulately connected to a connecting rod 56 which is similarly connected with a crank pin on the flange of the other valve member 49, i.e., of that valve member whichis received in the axial bore 50 of the other adjusting plunger 47 for the swash plate. The connecting rod56 performs a function similar to that of the connecting rod 38, namely; it insures that each angular adjustment of one of the two valvemembers 49 is commensurate with the angular adjustment of the other valve member 49 in order to guarantee that the swash plate is tilted in a manner as described in connection with FIG. 1 so as to reduce the volume of liquidfilled spaces of bores for the pump pistons to a minimum when the respective pistons reach the ends of their working strokes.

That portion of the illustrated valve member 49 which extends into the axial bore 50 of the. adjusting plunger 47 is provided with two helical grooves 58, 59 separated from each other by a rib 60. The width of the rib 60 equals the diameter of a channel 61 which extends radially outwardly from the bore 50 and communicates with the compartment 63 by way of an axially parallel channel 62. A second compartment 64 of the housing 45 (this compartment constitutes the righthand end portion of the cylinder. chamber 46 in the housing 45) is in permanent communication with a source of pressurized hydraulic fluid here shown as a motor-driven auxiliary pump 65. A channel 66 in the piston rod 48 connects the compartment 64 with one end of an axially extending ring-shaped chamber 67 in the piston rod 48. The right-hand groove 59 of the valve member 49 communicates by way of a radial bore 69 with one end of an axially parallel bore 68 provided 55 in the valve member 49 and communicating with a liquid collecting reservoir or tank 70. Another axially extending bore 71 of the valve member 49 has a first end which is in permanent communication with the groove 58 by way of a radial bore 72 and a second end in permanent communication with the chamber 67 by way of a radial bore 73. The reservoir 70 can'be formed by that part of the housing 45 which accommodates the swash plate and wherein the liquid is not under pressure.

The connecting rod 56 couples the two valve members 49 in such a way that a leftward movement of the illustrated adjusting plunger 47 entails a rightward movement of the other adjusting pl8nger or vice versa. This insures that the position of that piston which has completed its working stroke remains unchanged, i.e., that the volume of the liquid-filled portions of bores in the cylinder block is held to a minimum irrespective of the angular position of the swash plate.

The adjusting plunger 47 of FIG. 2 is at a standstill because the radial channel 61 is sealed by the rib between the grooves 58, 59 of the valve member 49. If the valve member 49 is turned in a clockwise direction, as considered from the right-hand side of the structure shown in FIG. 2, the inner end of the channel 61 in the adjusting piston 47 begins to Y communicate with the groove 59 whereby the compartment 63 communicates with the tank 70 by way of channels 62, 61, groove 59, radial bore 69 and axially parallel bore 68. Since the compartment 64 is connected with the outlet of the source of pressurized fluid, the adjusting plunger 47 moves in a direction to the left to expel fluid from the compartment 63 with attendant increase in the volume of the compartment 64. The adjusting plunger 47 comes to a halt when the inner end of its radial channel 61 returns into full registry with the rib 60 so that the compartment 63 is sealed from the tank to thereby prevent further inflow of pressurized fluid from the source 65 into the compartment 64. Thus, by selecting the extent of angular displacement of the valve member 49, an operator or an automatic programming system can change the inclination of the swash plate and hence the throughput of the axial piston machine without increasing the minimum liquid-filled volume of bores for the pistons in the cylinder block.

It the valve member 49 is rotated in a counterclockwise direction, as seen from the right-hand side of FIG. 2, the inner end of the radial channel 61 in the adjusting plunger 47 moves into registry with the helical groove 58. The source 65 is then free to admit pressurized fluid into the compartment 63 by way of the com partment 64, channel 66, chamber 67, radial bore 73,

axially parallel bore 71, radial bore 72, helical groove 58 and channels 61, 62.'Since the effective area of the surface at the left-hand end of the control plunger 47 (in the compartment 63) exceeds the effective area of the surface of the plunger 47 in the compartment 64, the plunger 47 begins to'move in a direction to the right so as to reduce the volume of the compartment 64 with a simultaneous increase in the volume of the compartment 63. This causes the swash plate to tilt in the opposite direction. The connecting rod 56 insures that the other control plunger 47 moves in a direction to the left while the illustrated plunger 47 moves in a direction to I the right. Such rightward movement of the plunger 47 shown in FIG. 2 is terminated when the inner end of the radial channel 61 returns into full registry with the rib 60 so that the compartment 63 is sealed from the groove 58 and hence from the source 65.

The axial piston machine of FIG. 3 is provided with adjusting means which constitutes a further modification of the adjusting means shown in FIG. 1 or FIG. 2.

Those parts of this machine which are clearly identical with or analogous to the corresponding parts of the machine shown in FIG. 1 are denoted by similar reference characters. The swash plate 23 is coupled to two tilting rods 76, 76' by links 26. The tilting rods 76, 76 form part of externally threaded feed screws or spindles 77, 77 and are reciprocable in bores 75, provided therefor in the housing 1. The links 26 hold the rods 76,

76' against rotation with reference to the housing 1 and the spindles 77, 77' respectively mesh with internally threaded nuts 79, 79' which are mounted in bores 80, 80' of the housing 1 for rotation but cannot move axially therein. The nuts 79, 79' are respectively connected with output members of electric adjusting motors or servomotors 78, 78' which receive signals from a control circuit 82. The latter is electrically connected with detectors 81, 81' which have scanning elements 83, 83' serving to detect the positions of the adjacent portions of the swash plate 23 and to transmit appropriate signals to the control circuit 82. The latter is adjustable, either by hand or by remote control, so as to rotate the servomotors 78, 78' in such a way that the spindles 77, 77' rotate in opposite directions whenever it becomes necessary to change the inclination of the swash plate 23. The nuts 79, 79' can form integral parts of the output shafts of the servomotors 78, 78'. The detectors 81,- 81' are mounted on the housing 1 in the region of the swash plate 23 and the housing is provided with suitable cutouts or openings for the scanning elements 83, 83'. The swash plate 23 can be tilted in a direction to merely change the (acute or obtuse) angle of inclination with reference to the axis of the drive shaft 4 or to change such angle from an acute angle to an obtuse angle or vice versa, i.e., to cause the fluid which was conveyed from the bore 42 into the bore 43 to flow from the bore 43 into the bore 42, or vice versa. A change in the magnitude of the acute or obtuse angle between the swash plate 23 and the axis of the drive shaft 4 merely entails a change in the throughput of the machine whereas a change from an acute angle to an obtuse angle or vice versa entails a change in the direction of fluid flow.

The signals from the detectors 81, 81' are utilizied to terminate the operation of servomotors 78, 78 when the inclination of the swash plate 23 has been changed to a desired extent, namely, to the extent indicated by the nature or intensity of input signal to the control circuit 82. The control circuit 82 can simultaneously serve as a regulator which insures that the changes in inclination of the swash plate 23 do not entail any changes or any appreciable changes in one or more characteristics (such as pressure) of the conveyed hydraulic fluid. Of course, the control circuit 82 further insures that the adjustment of the swash plate takes place with a view to guarantee constant clearance volume in the bores for the pistons when such pistons complete their working strokes and are located at a minimum distance from the valve plate of the axial piston machine.

The exact construction of the detectors 81, 81', servomotors 78, 78' and control circuit 82 forms no part of the present invention. Such devices are well known from the art and may respond to electrical, pneumatic or hydraulic signals.

The axial piston machine of FIG. 4 is provided with electronic adjusting means for the swash plate 23. The flow of fluid into and from cylinder chambers 28, 30 of the housing 1 is respectively controlled by electromagnetically operated valves 85, 85 These valves are connected with a source 65 of pressurized hydraulic fluid and with a tank or reservoir 70.

An electronic control circuit 86 has inputs 86a, 86b connected with the outputs of detectors 81, 81' and outputs 86c, 86d connected with the valves 85, 85. The scanning elements 83, 83' of the detectors 81, 81' scan the positions of adjacent portions of the swash plate 23 and transmit appropriate signals to the control circuit 86. The swash plate 23 is adjustable by plungers 27, 27 by way of tilting rods 29, 29' and links 26. The scanning elements 83, 83' are respectively adjacent to the upper and lower links 26, as viewed in FIG. 4, i.e., close to the points where the swash plate 23 is coupled to the tilting rods 29, 29'. The same applies for the embodiment of FIG. 3.

A third input 86 of the control circuit 86 can receive signals indicating the desired extent of adjustment of the swash plate 23. Such signals are used to actuate the valves 85, 85' in order to admit fluid from the source 65 into the cylinder chamber 28 while permitting fluid to flow from the chamber 30 into the tank or vice versa. The inflow of fluid from the source 65 into the chamber 28 (by way of the valve and simultaneous outflow of fluid from the chamber 30 into the tank 70 (by way of the valve 85') or vice versa is terminated when the signals from the detectors 81, 81' to the inputs 86a, 86b indicate that the swash plate 23 has assumed the desired angular position. The adjusting plungers 27, 27' can change the inclination of the swash plate 23 from a neutral position (shown in FIG. 4) to one of an infinite number of first positions in each of which the fluid flows from the bore 42 into the bore 43 or to one of an infinite number of second positions in each of which the fluid flows from the bore 43 into the bore 42. Such adjustments can take place without necessitating any changes in the direction of rotation of the shaft 4. The same holds true for the embodiments of FIGS. 1-3. The swash plate 23 of FIG. 4 always turns about the pivot axis between a follower 20 and the end portion 19 of that piston 18 which dwells in the foremost position (nearest to the valve plate 16). The plungers 27, 27' are of the double-acting type and each thereof constitutes a differential piston. The compart ments at the right-hand ends of plungers 27, 27' are permanently connected with the source 65.

It is equally within the purview of the invention to mount the adjusting means for the swash plate 23 in or on the cover 3, i.e., at that side of the swash plate which faces away from the cylinder block. In such machines, the swash plate is caused to pivot about an axis which intersects the axis of the piston dwelling in the foremost position. In other words, the axis of such piston would coincide with the axis of an element of the adjusting means. Such one element is then at a standstill while the other element moves the swash plate to a different angular position.

An important advantage of the improved axial piston machine is that the swash plate can be tilted to both sides of its neutral position by relatively simple, compact and rugged adjusting means without increasing the volume of the spaces which are filled with liquid in the foremost positions of the pistons.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for var ious applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of my contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

I claim:

1. In an axial piston machine, a combination comprising a cylinder block rotatable about a predetermined axis and having a plurality of axially parallel openended bores; a valve plate adjacent to said block to seal the open ends of said bores; pistons reciprocably received in said bores; a swash plate tiltable with reference to said axis to both sides of a neutral position to thereby change the extent of movement of said pistons with reference to said block in a direction away from said valve plate and to maintain said pistons at a predetermined minimum distance from said valve'plate in said neutral position thereof, one of said pistons being located at such minimum distance from said valve plate whenever said swash plate is tilted from said neutral position thereof; means for holding said swash plate against rotation with said cylinder block; andadjusting means for changing the inclination of said swash plate with reference to said axis, comprising a pair of movable tilting'members operatively connected with said swash plate at points located diametrically opposite each other with reference to said axis, and means for moving at least one of said tilting members to thereby tiltsaid swash plate about a second axis which intersects the axis of said one piston to thus insure that the axial position of said one piston remains unchanged in spite of the tilting of said swash plate.

2.,A combination as defined in claim 1, wherein said tilting members are movable in substantial parallelism with said predetermined axis.

3. A combination as defined in claim 2, wherein said means for moving said tilting members comprises a pair of-differential pistons.

4. A combination as defined in claim 3, wherein said differential pistons are connected with said tilting members and said adjusting means further comprises control means for moving said differential pistons.

5. A combination as defined in claim 4, wherein said control means comprises a pair of movable cams and connecting means for synchronizing the movements of said cams, said differential pistons having follower means tracking said cams.

6. A combination as defined in claim 4, wherein said control means comprises a pair of control pistons which are axially movable with reference to said differential pistons.

7. A combination as defined in claim 4, further comprising means defining for said differential pistons cylinder chambers, said differential pistons being movable axially by a pressurized fluidand said control means comprising rotary valve members arranged to control the flow of fluid into and from said chambers.

8. A combination as defined in claim 7, wherein said valve members have peripheral fluid flow controlling grooves and are rotatable with reference to said differential pistons, said adjusting means further comprising connecting means coupling said valve members for angular movements in synchronism with each other.

9. A combination as defined in claim 1, wherein said tilting members have threaded portions and said means for moving said tilting members comprises complementary threaded elements meshing with said threaded portions and means for rotating said complementary ele ments to thereby move said tilting members in substantialparallelism with said predetermined axis.

10. A combination as defined in claim'9, wherein said means for rotating said complementary elements comprises electric motors.

11. A combination as defined in claim 10, wherein said portions of said tilting members are provided with external threads and said complementary elements constitute internally threaded nuts meshing with said externally threaded portions.

12. A combination as defined in claim 1, wherein said adjusting meansfurther comprises signal generating detector means for scanning the position of said swash plate and for effecting the termination of movement of said tilting members when said, swash plate assumes a preselected position.

13. A combination as defined in claim 12, wherein said means for moving said tilting members comprises an electronic circuit receiving signals from said detector means.

14. A combination as defined in claim 13, wherein said means for moving said tilting members further comprises means defining a pair of cylinder chambers, electromagnetic valve means for regulating the flow of a pressurized fluid into and from said chambers in response to signals from said control circuit, and differential pistons reciprocably received in said chambers and connected with said tilting members. i

15. A combination as defined in claim 13, wherein said control circuit further comprises an input for signals indicating the desired extent of angular displacement of said swash plate.

#0 I I F 

1. In an axial piston machine, a combination comprising a cylinder block rotatable about a predetermined axis and having a plurality of axially parallel open-ended bores; a valve plate adjacent to said block to seal the open ends of said bores; pistons reciprocably received in said bores; a swash plate tiltable with reference to said axis to both sides of a neutral position to thereby change the extent of movement of said pistons with reference to said block in a direction away from said valve plate and to maintain said pistons at a predetermined minimum distance from said valve plate in said neutral position thereof, one of said pistons being located at such minimum distance from said valve plate whenever said swash plate is tilted from said neutral position thereof; means for holding said swash plate against rotation with said cylinder block; and adjusting means for changing the inclination of said swash plate with reference to said axis, comprising a pair of movable tilting members operatively connected with said swash plate at points located diametrically opposite each other with reference to said axis, and means for moving at least one of said tilting members to thereby tilt said swash plate about a second axis which intersects the axis of said one piston to thus insure that the axial position of said one piston remains unchanged in spite of the tilting of said swash plate.
 2. A combination as defined in claim 1, wherein said tilting members are movable in substantial parallelism with said predetermined axis.
 3. A combination as defined in claim 2, wherein said means for moving said tilting members comprises a pair of differential pistons.
 4. A combination as defined in claim 3, wherein said differential pistons are connected with said tilting members and said adjusting means further comprises control means for moving said differential pistons.
 5. A combination as defined in claim 4, wherein said control means comprises a pair of movable cams and connecting means for synchronizing the movements of said cams, said differential pistons having follower means tracking said cams.
 6. A combination as defined in claim 4, wherein said control means comprises a pair of control pistons which are axially movable with reference to said differential pistons.
 7. A combination as defined in claim 4, further comprising means defining for said differential pistons cylinder chambers, said differential pistons being movable axially by a pressurized fluid and said control means comprising rotary valve members arranged to control the flow of fluid into and from said chambers.
 8. A combination as defined in claim 7, wherein said valve members have peripheral fluid flow controlling grooves and are rotatable with reference to said differential pistons, said adjusting means further comprising connecting means coupling said valve members for angular movements in synchronism with each other.
 9. A combination as defined in claim 1, wherein said tilting members have threaded portions and said means for moving said tilting members comprises complementary threaded elements meshing with said threaded portions and means for rotating said complementary elements to thereby move said tilting members in substantial parallelism with said predetermined axis.
 10. A combination as defined in claim 9, wherein said means for rotating said complementary elements comprises electric motors.
 11. A combination as defined in claim 10, wherein said portions of said tilting members are provided with external threads And said complementary elements constitute internally threaded nuts meshing with said externally threaded portions.
 12. A combination as defined in claim 1, wherein said adjusting means further comprises signal generating detector means for scanning the position of said swash plate and for effecting the termination of movement of said tilting members when said swash plate assumes a preselected position.
 13. A combination as defined in claim 12, wherein said means for moving said tilting members comprises an electronic circuit receiving signals from said detector means.
 14. A combination as defined in claim 13, wherein said means for moving said tilting members further comprises means defining a pair of cylinder chambers, electromagnetic valve means for regulating the flow of a pressurized fluid into and from said chambers in response to signals from said control circuit, and differential pistons reciprocably received in said chambers and connected with said tilting members.
 15. A combination as defined in claim 13, wherein said control circuit further comprises an input for signals indicating the desired extent of angular displacement of said swash plate. 